This invention relates to an induction motor and, in particular, to an improvement of a three-phase induction motor combined with a deceleration mechanism to be used as a gear motor.
Existing induction motors used as a gear motor are classified into a single-phase induction motor and a three-phase induction motor. As the single-phase induction motor, a capacitor motor is known. In either event, a deceleration mechanism is directly coupled to an output shaft of the single-phase or the three-phase induction motor when it is used as the gear motor.
Generally, the single-phase induction motor is larger in volume and produces greater noise and vibration than the three-phase induction motor. In spite of the above-mentioned disadvantages, the single-phase induction motor is inevitably used in a place, such as an ordinary house, where three-phase AC is unavailable but single-phase AC alone can be used. It is therefore desired to suppress the noise and the vibration of the induction motor even in the place where the single-phase AC alone is available.
On the other hand, in case where the gear motor is provided, consideration must be made about the phase type of an available AC power supply, i.e., whether the gear motor is used with the single-phase AC or the three-phase AC. Thus, considering the potential use of the gear motor with the single-phase AC or the three-phase AC, both of the single-phase induction motor and the three-phase induction motor must be produced and kept in stock as induction motors each of which is to be combined with a deceleration mechanism. This means that a stock of the induction motors is increased in number and that a stock of parts for maintenance purpose is also increased in number. This is because those parts for both of the single-phase and the three-phase induction motors must be kept in stock.
Furthermore, the AC power supply has a frequency type. The frequency is, for example, 50 Hz or 60 Hz. In this case, the induction motor is operated at a single frequency of 50 Hz or 60 Hz. In order to obtain a desired rotation speed or rpm, a deceleration ratio of the deceleration mechanism must particularly and minutely be set.
In order to prevent burnout of the induction motor, a thermal relay must be provided separately from the induction motor.
It is therefore an object of this invention to provide a general-purpose induction motor adaptable for a user""s request or for a particular type of an AC power supply available in a local area where it is installed.
A general-purpose induction motor according to this invention includes a three-phase induction motor provided with a terminal box containing terminals for electrical connection. According to an aspect of this invention, the general purpose induction motor further comprises a conversion module contained in the terminal box and coupled to the three-phase induction motor. The conversion module has a function of converting a plurality of types of single-phase AC into a single type of three-phase AC so that the three-phase induction motor can be used with the single-phase AC.
The conversion module comprises a converter for converting the single-phase AC into DC, a capacitor for smoothing the DC as an output of the converter to produce smoothed DC, an inverter for converting the smoothed DC into the three-phase AC, a current/voltage detecting circuit for detecting a DC current/voltage to produce a current/voltage detection signal, a drive circuit for driving the inverter, and a first microcomputer for controlling the drive circuit in response to the current/voltage detection signal from the current/voltage detecting circuit.
The conversion module is coupled to a circuit board comprising a second microcomputer and having at least one of a frequency setting function, an acceleration/deceleration time setting function for soft start/stop, and an electronic thermal relay function.